Measurement of the Υ(1S), Υ(2S), and Υ(3S) polarizations in pp collisions at root s 7 TeV

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Abstract

The polarizations of the Upsilon(1S), Upsilon(2S), and Upsilon(3S) mesons are measured in proton-proton collisions at root s = 7 TeV, using a data sample of Upsilon(nS) -> mu(+)mu(-) decays collected by the CMS experiment, corresponding to an integrated luminosity of 4.9 fb(-1). The dimuon decay angular distributions are analyzed in three different polarization frames. The polarization parameters lambda(theta), lambda(phi), and lambda(theta phi), as well as the frame-invariant quantity (lambda) over tilde, are presented as a function of the Upsilon(nS) transverse momentum between 10 and 50 GeV, in the rapidity ranges vertical bar y vertical bar < 0: 6 and 0: 6 < vertical bar y vertical bar < 1.2. No evidence of large transverse or longitudinal polarizations is seen in the explored kinematic region.